This invention concerns an improved printed circuit heating element. The heating element is useful for the sterile welding of first and second thermoplastic tubes together transversely of the axis of each tube.
This invention represents an improvement in the heating element disclosed in U.S. Pat. No. 4,501,951. The heating element there disclosed was, in turn, an improvement over the heating element disclosed in U.S. Pat. No. 4,369,779. The heating element of U.S. Pat. No. 4,501,951 comprises an outer layer which is a folded sheet of metal; a resistor disposed inside said folded sheet of metal; a layer of dielectric adhesive between the inner surfaces of said folded sheet of metal and said resistor thereby electrically insulating the resistor from the folded sheet and bonding the resulting structure together; said resistor having exposed terminals for reception of electrical current and the folded edge of said metal sheet being the melting edge of the heating element.